The invention relates to a method of combustion or gasification of material containing composite components in a circulating fluidized bed which has a turbulence chamber for the combustion or gasification, a solids separator connected with the upper region of the turbulence chamber, a recycle from the solids separator of the deposited solids to the turbulence chamber and a cooling unit for the indirect cooling of solids which come from the solids separator, whereby the cooling unit includes a plurality of fluidized beds through which the solids migrate, one after the other.
The method of this type is known from WO 97 46 829 A1. Here the cooling unit is preceded by an uncooled fluidized bed whose flue gas is fed directly to the combustion. Because of this feature, the chloride concentration in the solids to be cooled are reduced. The chlorides are responsible for aggressive corrosive attack on the cooling unit. The known blowing through of the fluidized bed is above all not suitable in inappropriate cases, of lowering the chloride concentration of the solids to be cooled sufficiently to ensure the desired protection against corrosion. Especially corrosive are, for example, HCl encrustations on the cooling tubes.
The invention has the object of so treating the hot solids coming from the solids separator that their corrosivity in the cooling unit completely or substantially completely disappears. According to the invention this is effected in the method described at the outset in that the first fluidized bed into which the hot solids coming from the solids separator is first conducted is a dechlorination chamber whereby in this dechlorination temperature at a temperature of the solids in the range of 700 to 1100xc2x0 C. and in the presence of a fluidizing gas and at least one dechlorination additive which can be
a) a gaseous SO2 or a sulfur-containing material that liberates SO2 in an oxidizing atmosphere,
b) a silicate, laminate silicate,
c) activated silicate, or
d) other alkali additive compounds which liberate HCl, is added in at least a stoichiometric quantity to convert the alkali and metal chlorides contained in the supplied solids.
As solid additives, various aluminum silicates, for example, kaolinite have proved to be effective. Also suitable are activated silicates (for example commercial ICA 5000), whereby the activation is achieved by boiling in sodium hydroxide. Economical is the use of waste substances, for example, chloride-free clarifier sludge or contaminated earth which contain these additives.
The reaction capabilities of the silicate, aluminum silicates, or the activated silicates depends substantially upon the hydroxyl groups on the silicon. These additives bind the alkali and metal in the hot solids so that chlorine is liberated as HCl which is less corrosive than, for example, alkali or metal chlorides. Usually these solid additives are fed in powder form into the fluidized beds whereby the mean particle size d50 lies approximately in the range of 50 to 500 xcexcm. A gradual supply of the solid additive to the feed line of the hot solids is also possible.
Gaseous SO2 is above all suitable for reaction with alkali chlorides or metal chlorides in a vapor form and thus to form sulfate and HCl in the presence of molecular oxygen. The liberated HCl is driven off with the fluidizing gas from the dechlorination chamber. Sulfates are not corrosive or are scarcely corrosive and can be disposed of with the ash discharged from the process.
One can supply SO2 in the gas space in a molar concentration of 0.25 to about 6 times the concentration of the liberated HCl. The SO2 can also be introduced as sulfur-containing materials which release SO2 at the higher temperatures in the dechlorination chamber or liberate SO2 in oxidizing atmospheres.
The fluidized bed in the dechlorination chamber can operate with or without indirect cooling; usually this fluidized bed is maintained free from an indirect cooling. The remaining fluidized beds in the cooling unit contain heat exchangers provided by liquid gas or vapor coolants. By eliminating or at least reducing the corrosivity of the hot solids, one can maintain the temperature in the hottest fluidization bed high which, for example, can benefit the vapor superheating.
The material to be combusted or gasified can be of different types. It can thus be, for example, coal, lignite, biomass (e.g. wood or straw), solid and/or liquid wastes or clarifier sludge whereby, in addition, several of the aforementioned materials can be mixed.